Well since SEPA specifically refers to Philly metro and suburbs most of the time, anything west of that usually calls itself 'Central' even if its on the eastern side of the state. South Central PA is odd, The eastern part forms the core of Dutch Country, the western part you are more in the Appalachian foothills, and then in between you have the capital region.

There's even a regional planning org(http://www.southcentralassembly.org/)